Saving projects to more than one file or path
I am not aware of any way to do that by default. That's why wrote a little add-on for you.

The add-on allows you to create a list of paths that the file should be saved to. Then every time a render is written to disk it is automatically copied to the specified paths.

The add-on can be downloaded here: https://github.com/oweissbarth/blender_multisave/releases/download/0.0.1/multisave_0_0_1.zip

To install the add-on click on "Edit" > "Preferences" > "Add-ons" > "Install..." and select the downloaded zip file and click "Install Add-on". Then activate the add-on by clicking on the checkbox next the its name.


The add-on will then appear in the properties editor in the output tab as its own panel called "MultiSave". You can add a new path to save to by clicking the "plus"-icon.  You can change the path of an item by double clicking it. And finally you can remove an item by selecting it from the list clicking the "x"-icon.



The source code is on github: https://github.com/oweissbarth/blender_multisave/